1. Technical Field
This invention relates in general to electronic circuits and, more particularly, to circuitry for reducing the skew between two signals.
2. Description of the Related Art
In the design of electronic circuits, it is often necessary to compensate for skew between two signals arriving at a common block. Traditionally, the skew between the two signals is reduced with the addition of buffers to equalize the difference between the paths of the two signals. Often, the appropriate buffers can be determined automatically using computer aided design tools.
An example of the problem is set forth in connection with FIGS. 1a and 1b. FIG. 1a illustrates an example a portion of an integrated circuit where signals from two different circuitry blocks (source blocks) are received at a third block (user block). First source block 10 is clocked using clock Ca and a second circuitry block 12 is clocked using clock Cb. First and second source blocks 10 and 12 could implement any type of analog or digital circuitry, or a mix thereof. As shown in FIG. 1b, Clocks Ca and Cb are skewed by an amount Skew(Ca−Cb). The output A of source block 10 is delayed by a time Da due to propagation through the logic of source block 10 and routing delays between the output of source block 10 and the input to user block 14. Similarly, the output B of source block 12 is delayed by a time Db due to propagation through the logic of source block 12 and routing delays between the output of source block 12 and the input to user block 14. For reference, FIG. 1b is a timing diagram which shows the skew between clocks Ca and Cb at the inputs to source blocks 10 and 12, respectively, and shows the delay between the resulting signals at the input to user block 14. This delay is a factor of the skew between clocks Ca and Cb and the delays Da and Db. The delay between signals A and B at the input to user block 14 could be defined as:Delay(A−B)=Skew(Ca−Cb)+Db−Da 
In mixed signal design, there will be digital spread delays and analog spread delays. The spread of each cannot be easily compensated with a unique addition of digital delay.
Therefore a need has arisen for a method and circuit for reducing skew between two signals.